Conventionally, there has been known a mobile communication system including a plurality of radio base stations. For example, as such a mobile communication system, LTE (Long Term Evolution) has been known.
Furthermore, as a process cooperatively performed by the plurality of radio base stations, a handover, a cooperative reception process, a cooperative transmission process and the like are considered. The cooperative reception process and the cooperative transmission process are called CoMP (Coordinated Multi-Point Operation) and the like.
As described above, in the process cooperatively performed by the plurality of radio base stations, it is necessary to achieve synchronization between each of the plurality of radio base stations and a radio terminal. In this regard, in the process cooperatively performed by the plurality of radio base stations, a procedure for achieving the synchronization between each of the plurality of radio base stations and the radio terminal is defined.
However, a case in which synchronization was already achieved among the plurality of radio base stations is also assumed. In such a case, the procedure for achieving the synchronization between each of the plurality of radio base stations and the radio terminal is redundant.